Protein hydrolysates are mixtures of polypeptides, oligopeptides and/or amino acids that are man-ufactured from protein sources using partial or complete hydrolysis. There is a growing interest in protein hydrolysate preparations which have many uses, e.g., in human nutrition, e.g., as ingre-dients in energy drinks, weight-control and sports nutrition products, as a source of nutrition for elderly and underweight patients, and in the flavour industry. The protein could be derived from plants, e.g., soy, wheat or corn, or from animals, e.g., milk, eggs, meat or fish.
Production of protein hydrolysates in the food industry involves enzymatic, acid or alkali protein hydrolysis. Chemical hydrolysis is difficult to control and reduces the nutritional quality of the products. Enzymatic hydrolysis works without destructing amino acids and by avoiding the extreme temperatures and pH levels required for chemical hydrolysis, the nutritional properties of the protein hydrolysates remain largely unaffected.
However, for enzymatically hydrolysed protein, the protein yield and the degree of hydrolysis (DH) obtained are often limited.
A key factor limiting the yield and degree of hydrolysis is the conformation of the substrate protein to be hydrolysed. Not unfolded proteins, e.g. globular proteins, will often be more difficult to degrade than unfolded proteins, as it is more difficult for the proteases to degrade folded proteins. A variety of reagents and conditions can cause denaturation and result in the disruption of the secondary and tertiary structure of the protein. Heat can be used to disrupt hydrogen bonds and non-polar hydrophobic interactions a.o. being responsible for the secondary- and tertiary structure; the heating causes the molecules to vibrate so rapidly and violently that these bonds/interactions are disrupted.
It is common practice to unfold or denature the substrate protein by performing a heat treatment before addition of the proteolytic enzymes; however this is not an optimal method as the unfolding or denaturation often requires a high temperature at which the proteolytic enzymes applied are not stable and/or not at their optimum for activity. Especially the exopeptidases have a low thermostability. Lowering the temperature after unfolding will enable the proteins to re-aggregate in a way which will reduce the efficiency of the proteolytic degradation.
It is an object of the present invention to provide protein hydrolysates having improved properties, such as a high solubility, a high degree of hydrolysis, a high protein yield and/or a pleasant flavour.